This invention relates, in general, to optical devices, and in particular, to diffraction gratings.
Diffraction gratings have been made and used for a long time. Generally, diffraction gratings are vertical parallel periodic structures. Spacing of these vertical parallel structures is usually on the order of a wavelength of an illumination source. When commonly used, the diffraction grating is illuminated by optical electromagnetic radiation, resulting in a spectra being produced. Recently, diffraction gratings have begun to be investigated for use with semiconductor products.
Conventionally, vertical diffraction gratings that are used with semiconductor products are manufactured by treating a photopolymer film with two light sources. Generally, these light sources originate from a single laser beam that has been split into two halves to form two beams. The two beams are then redirected onto the photopolymer film so that the two beams meet at the same area on the photopolymer film. By directing the two beams onto the photopolymer film, constructive and destructive waves are formed that periodically change the photopolymer film chemically in some areas, but do not chemically change the photopolymer film in other areas, thereby producing the vertical diffraction grating in the photopolymer film. The vertical diffraction grating that is produced, however, has several major problems, such as not being sufficiently sensitive, being able to produce only vertical periodic structures, and not being able to be integrated easily into semiconductor products.
Efficiency of a diffraction grating is measured by comparing an amount of light that is diffracted by the grating to an amount of light that is directed into the grating. The inefficiency of conventional diffraction gratings generally are due to a small refractive index difference between the periodic structures that are formed in the diffraction gratings. Using the conventional method of fabricating a diffraction grating, it is very difficult to increase or to change the differences of refractive indexes between the periodic structures of the photopolymer film. Further, sharp clear-cut divisions between the periodic structures are not possible to produce with the conventional process, thus further reducing the efficiency of the diffraction grating.
Additionally, the conventional diffraction gratings that are manufactured with the photopolymer film do not allow for any profile modification of the periodic structures. This inability to modify the profile of the periodic structures further curtails or restricts using conventional diffraction gratings, as well as modifying the sensitivity of conventional diffraction gratings.
It can be seen that conventional methods for producing diffraction gratings have several limitations. Also, it is evident that conventional diffraction grating structures are not capable of fulfilling recent requirements that are needed for use in semiconductor products, because conventional diffraction gratings are not easily integrated into semiconductor products. Therefore, a method for making an angled diffraction grating would be highly desirable.